2027 ICD-10-CM Diagnosis Code Q23.4Hypoplastic left heart syndrome
ICD-10-CM Codes›Q00-Q99›Q20-Q28›Q23
- Billable — Valid for Submission
- MCC — Major Complication or Comorbidity
- POA Exempt
- Chronic Condition
Q23.4 is a billable ICD-10-CM diagnosis code for hypoplastic left heart syndrome. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 306 through 307. As a secondary diagnosis, it counts as a major complication or comorbidity (MCC) and places an inpatient stay in the highest severity level of its MS-DRG family. It does not count, however, when the principal diagnosis is one of 68 closely related codes. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac and circulatory congenital anomalies.
Q23.4 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model. It still risk-adjusts in the RxHCC Part D (V08) category 191 for payment year 2027.
Code Identity
Code Classification
Present on Admission (POA)Billing
Q23.4 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Congenital malformations of the circulatory system (Q20-Q28).
Medicare Risk Adjustment (HCC)Billing
Q23.4 does not risk-adjust for Medicare Advantage under the CMS-HCC V28 model, but it maps to payment categories in the other CMS models shown below.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Hypoplastic left heart syndrome
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to Q23.4: its own notes plus those printed at Chapter 17. A note printed at a category, block or chapter applies to every code under it.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Notes
General instructions on how these codes are used.
- Codes from this chapter are not for use on maternal records
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name Q23.4, its category, or a range that includes it.
Excludes1 2
These codes carry an Excludes1 note naming Q23.4: they are not reported together with it, unless the two conditions are unrelated.
Excludes2 1
These codes carry an Excludes2 note naming Q23.4: its condition is not part of those codes, and both may be reported when the patient has both.
Use Additional Code 1
These codes say to use an additional code from the note, and Q23.4 is one of the codes named.
- Q87.88 CTNNB1 syndrome
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
defective, congenital See Also: Anomaly, by site;
Syndrome See Also: Disease;
hypoplastic left-heart Q23.4
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Hypoplastic Left Heart Syndrome
a condition caused by underdevelopment of the whole left half of the heart. it is characterized by hypoplasia of the left cardiac chambers (heart atrium; heart ventricle), the aorta, the aortic valve, and the mitral valve. severe symptoms appear in early infancy when ductus arteriosus closes.
Patient EducationClinical
Congenital Heart Defects
Congenital heart defects (CHDs) are problems with the structure of the heart. "Congenital" means that that the problems are present at birth. These defects happen when a fetus's heart doesn't develop normally during pregnancy. Congenital heart defects are the most common type of birth defect.
The full article covers:
- What are congenital heart defects?
- What causes congenital heart defects?
- Who is more likely to have a baby with a congenital heart defect?
- What are the symptoms of congenital heart defects?
- What other problems do congenital heart defects cause?
- How are congenital heart defects diagnosed?
- What are the treatments for congenital heart defects?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert Q23.4 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About Q23.4Overview
What is the ICD-10 code for hypoplastic left heart syndrome?
The ICD-10-CM code for hypoplastic left heart syndrome is Q23.4 (sometimes written as Q234). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is Q23.4 (Congenital malformations of aortic and mitral valves) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report hypoplastic left heart syndrome on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does Q23.4 group to?
When hypoplastic left heart syndrome is the principal diagnosis on an inpatient stay, it groups to MS-DRG 306, 307, with relative weights from 0.9146 to 1.5457 depending on complications. Higher weights mean higher Medicare reimbursement.
Is Q23.4 a CC or MCC?
CMS lists Q23.4 as an MCC (major complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it places the inpatient stay in the highest-weighted DRG of its severity family. It does not count when the principal diagnosis is one of the 68 closely related codes in its exclusion list.
Is Q23.4 exempt from POA reporting?
Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for hypoplastic left heart syndrome on inpatient claims. The code appears in the Congenital malformations of the circulatory system (Q20-Q28) range of the CMS exempt list.
Does Q23.4 risk-adjust for Medicare Advantage payment?
Not for Medicare Advantage: Q23.4 maps to no category in the CMS-HCC V28 model. It still risk-adjusts in the RxHCC Part D (V08) category 191 (Ventricular Septal Defect and Major Congenital Heart Disorders).
